1. Field of the Invention
The present invention relates to a semiconductor laser device and an optical pickup device, and it particularly relates to a semiconductor laser device and an optical pickup device both employing a semiconductor laser element.
2. Description of the Related Art
The semiconductor laser element is conventionally in widespread use as a light source of an optical disk system, an optical communication system and the like. In particular, a semiconductor laser element emitting a laser light in the visible light band of about 380 nm to about 780 nm is in practical use as the light source for the recording and playback/reproduction of various types of optical disks for use in CD, DVD, BD and so forth. In recent years, along with the price reduction in the optical disk systems, it is expected nowadays that the overall size and the thickness of a light source unit built in the optical disk system be reduced.
In the conventional practice, a semiconductor laser device in which the laser light is emitted to the semiconductor laser element and reflected upward so as to be emitted externally is known as the above-described semiconductor laser device used as the light source (See Reference (1) and Reference (2) in the following Related Art List, for instance).
Reference (1) discloses a semiconductor laser device equipped with (i) a silicon substrate, on which a recess in a stepped shape is provided, and (ii) a semiconductor laser element placed on the silicon substrate. In this semiconductor laser device as cited in Reference (1), the semiconductor laser element is placed on a bottom face of the recess (stepped portions) formed in the silicon substrate. Also, a tilted side surface (reflection mirror surface) that connects a surface (top face), on which side the recess is opened, to the bottom face of the recess is formed in the silicon substrate. And the semiconductor laser element is placed so that an emission edge surface of the laser light is positioned counter to the tilted side surface (reflection mirror surface) of the silicon substrate and separately apart therefrom by a predetermined distance. In this manner, the arrangement according to Reference (1) is such that the laser light emitted from the emission edge surface is reflected upward by the tilted side surface (reflection mirror surface) and then emitted externally. In this semiconductor laser device, the top face of the semiconductor laser element is protrudingly positioned above the surface (top face) on which side the recess of the silicon substrate is opened.
Reference (2) discloses an optical semiconductor device (semiconductor laser device) including (i) a semiconductor laser element placed on the bottom face of a package, having an opening therein, made of a resin, (ii) a transparent substrate that covers the opening of the package, and (iii) a mirror bonded on an underside of the transparent substrate and mounted within the package. In this optical semiconductor device as cited in Reference (2), the emission edge surface of the laser light in the semiconductor laser element is positioned counter to the reflection surface of the mirror and separately apart therefrom by a predetermined distance. In this manner, the arrangement according to Reference (2) is such that the laser light emitted from the emission edge surface is reflected upward by the reflection surface of the mirror and then emitted externally, so that thickness of the semiconductor laser device can be reduced.